Grinders and similar abravise tools, milling cutters and the like may be named as examples of rotary tools of the kind in question. The nickel layer protects the machining portion from corrosion and bonds the diamond particles to the machining portion. Yet nickel layers are relatively soft and tend to wear easily. During use of the tool, it is the diamond particles which do the cutting work and, therefore, suffer the greatest stress. Even so the stress in the circumferential surface of the machining portion still is great, particularly due to the resulting chips so that the nickel layer wears off in the course of the time of use.
It was found that the wear described of the machining portion may result in loosening of the diamond particles in the nickel layer from which they may become detached, thereby rendering the tool useless.
It is generally known to increase the corrosion resistance and surface hardness of work pieces by providing them with a chromium nitride coat.